java Annotation 拼装SQL语句(转)

最新推荐文章于 2024-06-29 00:02:11 发布

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本文介绍了一个使用Java反射和自定义注解构建SQL查询字符串的例子。通过在类和字段上应用@TableRef和@FiledRef注解，可以方便地从Java对象生成对应的SQL语句。

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.Field;

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@interface FiledRef
{
    String fieldName();
}

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@interface TableRef
{
    String tableName();
}

@TableRef(tableName = "MobDevice")
public class ReflectTest
{
    @FiledRef(fieldName = "ID")
    private Long id;

    @FiledRef(fieldName = "DEVICE_NAME")
    private String name;

    @FiledRef(fieldName = "DEVICE_CODE")
    private String code;

    public ReflectTest(Long id, String name, String code)
    {
        this.id = id;
        this.name = name;
        this.code = code;
    }

    public Long getId()
    {
        return id;
    }

    public void setId(Long id)
    {
        this.id = id;
    }

    public String getName()
    {
        return name;
    }

    public void setName(String name)
    {
        this.name = name;
    }

    public String getCode()
    {
        return code;
    }

    public void setCode(String code)
    {
        this.code = code;
    }

    /**
     * @description
     * @author zhangml
     * @date May 17, 2010 4:39:30 PM
     * @param args
     */
    public static void main(String[] args)
    {
        ReflectTest rt = new ReflectTest(new Long(1), "2", "3");
        StringBuffer sql = new StringBuffer("");
        buildSql(rt, sql);
        System.err.println(sql);
    }

    public static void buildSql(Object obj, StringBuffer sb)
    {
        Class<? extends Object> clazz = obj.getClass();
        Field[] fields = clazz.getDeclaredFields();
        if (clazz.isAnnotationPresent(TableRef.class))
        {
            TableRef tr = (TableRef) clazz.getAnnotation(TableRef.class);
            sb.append("SELECT * FROM ");
            sb.append(tr.tableName());
        }
        if (fields != null && fields.length > 0)
        {
            sb.append(" WHERE ");
            for (Field field : fields)
            {
                try
                {
                    Object value = field.get(obj);
                    if (value != null && field.isAnnotationPresent(FiledRef.class))
                    {
                        FiledRef fr = field.getAnnotation(FiledRef.class);
                        sb.append(fr.fieldName() + "=" + value);
                        sb.append(" AND ");
                    }
                }
                catch (Exception e)
                {
                    e.printStackTrace();
                }
            }
            int length = sb.length();
            sb.delete(length-5, length);
        }
    }

}

执行结果：SELECT * FROM MobDevice WHERE ID=1 AND DEVICE_NAME=2 AND DEVICE_CODE=3